Two-week cranberry course gives six months protection against bladder infections
Women who are susceptible to cystitis can improve their resistance by eating 42 g dried cranberries daily, write urologists and nutritionists at the University of Wisconsin in Nutrition Journal. A two-week course will have a six-month effect.
Cranberry is a tried and tested remedy for urinary tract infections. The theory goes that it's the phenols in cranberries, such as trans-cinnamaldehyde [structural formula shown below], that weaken bacteria, making it more difficult for them to attach themselves to the wall of the bladder. [J Urol. 2011 Apr;185(4):1526-31.] [BMC Microbiol. 2008 Sep 16;8:149.] [PLoS One. 2011 Jan 13;6(1):e16084.]
This theory still holds, but recent meta-studies have concluded that a course of cranberries only reduces the chance of an infection by ten to twenty percent. [Cochrane Database Syst Rev. 2012 Oct 17;10:CD001321.] That's not much.
One factor that plagues these studies, however, is the high dropout rate. It seems that people find it difficult to sustain cranberry consumption over a longer period. Studies in which cranberry supplements were used instead have not been an unqualified success either - possibly because these supplements contain too small amounts of active ingredients.
This is the background against which the study was published in Nutrition Journal. It was financed by Ocean Spray Cranberries, the supplier of the sweetened and dried cranberries that the researchers gave to 20 women who suffered from repeated urinary tract infections.
The researchers got the women to eat 42 g cranberries daily for two weeks. They then monitored the women for six months, noting when the women had an infection.
The figure on the left below shows that most of the women had fewer infections in the six months after the cranberry course [6 month UTI-Rate] than in the six months preceding the treatment.
The figure on the right above shows that the women in the experimental group were less likely to develop an infection than the women in the control group. Half of the women in the experimental group remained infection free in the six months after taking the cranberries.
The researchers took samples of the bacteria in the women's rectum and analysed them. They expected that the cranberries would have reduced the amount of bacteria that cause urinary tract infections, but they found no relevant effects.
The researchers suspect that cranberries contain bioactive substances that strengthen women's immune systems, enabling them to better fight harmful bacteria. Animal studies have shown this to be the case. [JPEN J Parenter Enteral Nutr. 2014 Jan;38(1):107-14.] There is also a human study – funded by Ocean Spray – in which cranberries had a protective effect against viruses.
"The results of this study indicate a potential beneficial effect of consuming sweetened, dried cranberries in reducing the number of recurrent urinary tract infections in susceptible women", the researchers conclude.
"However, the results shown here are only preliminary and further studies are necessary. Daily sweetened, dried cranberry consumption is an inexpensive and readily available supplement to a woman's diet and may provide potential prophylactic effects."
Nutr J. 2013 Oct 18;12(1):139.
Animal study: cranberries are an anti-aging drug 19.03.2014
Cranberries help immune system fight colds and flu 17.01.2014
Cranberries help liver clear more cholesterol out of your blood 05.12.2008